Public address system



i. F. DURST ET AL PUBLIC ADDRESS SYSTEM Dec. 6, 1938.

'5 Sheets-Sheet 1 Filed May 28, 1936 INVENTOR. 9 F Duns? 5cm! 1 Be fiberf- 3,;

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I. F. DURST ET AL PUBLIC ADDRESS. SYSTEM Filed May 28, 1956 Dec. 6, 1938.

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-UNITE'D STATES 2,139,006 7 PUBLIC ADDRESS SYSTEM Irving F. Durst, Great Neck, and Semi Joseph Begun and Herbert Barnett, New York, N. Y., I assignors, by mesne assignments, to Carll Tucker, New York, N. Y. i

\x Application May 28, 1936, Serial No. 82,244

\ 25 Claims.

This invention relates to improvements in signaling systems of the type commonly known as public address systems, with particular relation to the application of such systems to shipboard.

The basic object of this invention is to provide a public address system for use on board ship having circuit characteristics which greatly increase the dependability of the system both under normal and emergency conditions.

More specifically the invention consists in the application of a signaling or public address system to a conductive network comprising the three-wire neutrals and the normal and emer gency wiring circuits commonly employed on shipboard to providea plurality of channels over each of which the signal energy may be transmitted to operate signal responsive devices common to all the channels.

A still further object of the invention is to incorporate the signal responsive devices in a system of this type whereby the grounding or short circuiting'of portions of the system or of some of the signal responsive devices does not' operate to render the remainder of the system and the remainder of the signal responsive devices inoperative.

These and many other objects as will appear from the following disclosure are secured by means of this invention:

This invention resides substantially in the combination, construction, arrangement, and rela- 1 tive location of parts, all as will be setforth in the necessary detail in the following specificav tion.

In the accompanying drawings,

Figure 1 is a diagrammatic view of one form of system in accordance with this invention as applied on board ship;

Figure 2 is a similar view of a modified arrangement particularly with respect to the connection of the signal responsive devices to the multichannel network;

Figure 3 isa diagrammatic modification of the arrangement of Figure 1 somewhat simplifled;

Figure 4 is a digrammatic layout of a modification of a portion of the system for employing automatic means for switching any impedselective, groups thereof.

' operative.

Figure '7- is a diagrammatic illustration of a further modified form'of system employing the principles of this invention. 6*

In the cause of safe-and dependable operation of ships at sea,-and particularly in emergencies, it is highly desirable to provide. a signaling system by meansof which the oflicers on the bridge, or at other control points on a vessel be able to 10 issue orders to the entire ship, that is to the crew and passengers, or to either selectively, or to Any such system applied on shipboard finds its maximum utility at times of emergency only if the signaling system 151 is so constructed and installed that in times of emergency it maybe depended upon to function normally. It is believed that heretofore no such system has been available. p

The normal signaling or public address sys- 20 tems employed on land areparticularly'vulnerable iunder emergency conditions, and are not at all adapted to use on shipboard. Wiring circuits on board ship evenwunder normal conditions are notoriously subject to undesired grounds 25 and short circuits of a nature which would render the ordinary signaling systems if not inoperative, highly uncertain. Likewise in cases of 1 emergency on shipboard the ordinary signaling system which provides but a'singletransmitting 30 channel is particularly vulnerable to complete inoperability because of the possibility of the interruption of the circuits.

The system of this invention is characterized by unusual dependability not only under normal, but also under the most adverse emergency conditions because it is characterized first bythe fact that it comprises a plurality of channels over any one ofwhich the signal energy may travel to the signal responsive'devices in spite 40 of interruption of the other channels, and secondly because undesired grounds and short circuits and defective signal responsive devices do not render the other, signal responsive devices in- These broad features will become apparent in several specific applications from the following description.

In Figure l a portion of a ships hulland superstructure is diagrammatically illustrated at I Modern sailing vessels are commonly equipped with two power supply sources. which may be termed the normal and emergency sources for supplying electric energy for the operation of the electrical equipment carried by the vessel. At 2 and 3 are diagrammatically illustrated generators which are connected to supply a three-wire system comprising the circuit wires 4 and 5 and the neutral 6. For purposes of simplicity the circuit wires 4 and 5 have not been shown extended to various parts of theyessel since they are notinvolved in this invention. Neutral 6 is shown grounded to the hull of the vessel through a resistance l which is commonly present in the grounding connection. The neutral 6 is shown running on one deck level to the various parts of the ship by the wire 1. Similarly this neutral is shown extending to the various parts of the ship on the other deck levels, as indicated at 8 and 9. These neutrals are connected as shown to the common neutral wire 6. I

v On the bridge or at some other suitable point on the upper deck of the ship, as is common practice, are the emergency generators H and 12 which are provided with their own wiring system independent of the wiring system fed by the generator's 2 and 3. The emergency wiring system comprises conductors l3 and I 4 which as before are not' shown extended to the various parts of the ship, and a common neutral l5. This neutral is, provided with the branch neutrals I6, I! and 18 at the various deck levels,and connected thereto by the leads l5, l5 and I5 respectively. As is common practice, on shipboard, the neutrals 6 and I5 may be connected together. This has been indicated by the wire I and the switch 20. In

accordance with this invention there is included in the connection between the neutrals an impedance coil 2|,which offers little resistance to the flow of power currents between the two systems from the normal and emergency sources. However, this impedance 2! isselected so as to have a high value with respect to the signal currents so as not to form a low impedance shunt'fo'r the source of signal energy. Thus whether switch 20 is open or closed does not substantially affect the signal level on the neutrals.

At 22 is a microphone or other suitable form of signal device feeding into any suitable and well known form of amplifier which has been diagrammatically indicated at 23. Preferably the output of the amplifier is fed into two or more separate transformers of which by way of examplc the secondaries 25 and 24 are shown. In

view of statements made later it would be well to state that secondaries 25 and 24 may be connected in parallel so that the two main feeders havegti e same polarity, or inseries so that the polarity of the two feeders is opposite with respect to ground. Each connection has apparent advantages and disadvantages. One terminal of each is shown with a common grounding connection 26 grounded on the hull. Under some conditions single transformers can be used with grounded tapped secondary. The other terminals of the secondary are connected through the condensers 21 and 28 to the neutral wires as shown. Thus condenser 21 is connected by wire I!) directly to the neutral l and condenser 28 is connected by the wire ID to the wire l0 which extends to the other neutral 6. In other words, the wires i9 and III are connected to the neutral system on opposite sides of switch 20 and coil 2|.

The signal responsive devices are connected across the two neutral wire systems. Thus, on the upper deck the neutrals l6 and 9 provide a conductive network for the signal responsive devices on that level. Connected across the wires 9 and I6 at the desired points are the primaries single transformer with a mid-tap, are grounded to the hull by the wire 3 I.

It is preferable to employ two separate transformers as distinguished from a single transformer having a mid-tap. This is desirable in order that if one of the lines to the speaker transformers is grounded a complete short circuit of the speaker will not result. Where a single transformer with a mid-tap is used a ground on one of the lines will either short'the other circuit to the speaker or substantially reduce the volume of sound output therefrom. For this reason two separate transformers are preferably connected as illustrated so that the grounding of one of the lines will not interfere with the power volume operation of the associated speaker. The outside terminals of the primary are connected to the neutrals l6 and 9 through the condensers 32 and 33. The secondaries of the transformers 29 and 30 are connected in series with a signal responsive device 34, such as a loud speaker.

In accordance with this invention it is important that the speaker transformers 29 and 30 have together a small impedance of the order of 3 or 4 ohms so that the impedance of the speakers is matched with the impedance of the conductors, so that when'one or more transformers and/or associated condensers and/or conducting channels are short circuited none of the speakers are affected and all remain operative. Thus only a short circuit directly across the secondaries of transformers 29 and 30 will render a speaker inoperative if the secondaries of transformers29 and 30 are connected in series, and then only that particular loud speaker. The impedance in the circuit between any two speakers is always normally high enough so that a short circuit on one of the speakers does not render the adjacent speakers inoperative.

The above statement is true if the main feeders are fed from both ends as illustrated in Figure 1 with respect to all of the speakers connected thereto so that there is a'potential drop between any other point on the feeders and the grounded point. For this reason it is desirable, as illustrated in Figure 1,-to apply the signal energy from the extreme ends of each associated pair of feeders or neutrals. The other speakers on the same level and onthe other levels are similarly connected between the neutrals. The dotted lines marked P represent the various metallic partitions or bulk heads in the hull of the vessel, and it is on these that the various speakers have been indicated as grounded.

In the normal operation of this system the signal energy is impressed over thecondensers 21 and 28 and wires l9 and I0 onto the two neutral systems radiating from the neutrals l5 andfi. The other terminals of the output transformer impress the energy onto the hull of the ship through the grounded lead 26. Thus energy is supplied to each of the signalresponsive devices independently over each of the neutrals and the hull of the ship to the grounding terminals 3!.

In normal operation therefore the speakers are supplied with signal energy over both circuits. In the event that either circuit fails energy will be supplied nevertheless over the other circuitto the signal responsive devices. Thus for example, if the connection l5 to the neutral I6 is accidentally or unintentionally grounded or short circuited, or opened, as indicated by the numeral F, the signal energy will be supplied from the amplifier 23 over the neutral 6, and its branch 9 to ground so that the speakers 34 connected thereto will operate. Again, it both neutral branches l and I1 have an accidental ground on them-as indicated in dotted lines at F, all of the loud speakers will operate. Energy will be suppliedto all of the speakers even with 'adirect short circuit across the primaries 0! transformers 29 and 30 or their respective feeders when"*each-speaker is fed through parallel circuits andlthereiore, there is always a potential diflerence between these circuits and ground. Here, asdescribedabove, the

statement in the preceding sentence is true for all speakers connected to each pair-oi neutrals where thesignal energy is applied to both ends of the circuit wires. A similar thing will occur if an accidental ground occurs on one or both of the neutral conductors 1 and was indicated by the reference numeral F on the lower level, indicating accidental grounding of both'of these neutrals. In the event that themain power generators 2 and 3 and their circuits become inoperative during an emergency at which time the normally closed switch 20 is open, the signal energy is still sent over all neutral circuitsand their'branches to effect operation of all of the loud speakers. Thus the system works whether or not switch 20 is open .or closed, and whether'or not one or the other of the circuits comprising the normal and emergency neutrals and their branches are inoperative either in part or in whole.

In the system of Figure 2 the neutral 6' of the generators 2 and 3 is connected by the various branch neutrals :1'-, 8', 9'., I0; H3 12, l3; l4 and HP. The neutral l5'-of the emergency generators H and i2 is connected through branch neutrals 5|, 53, Hand .51 and the emergency circuit. Neutral 5| is connected in: a junction box Bto the normal neutral system through condenser 52 and similarly emergency neutral 53 is connected to the normal neutral system through condenser. 54, emergency 51=is connected through 58 to thenormal, and emergencyfl is connected through the condenser 59 to the normal neutral system. Emergency neutral I5". is connectedto the normal neutral 6' through a normally closed switch 20 and the connection 10*, which is opened only -in,case of emergency. The microphone as before feeds intoan amplifier 23 of any suit able form, which in this case is provided with two distinct output transformers 24 and 25. Thesesondaries 44 and 45 of these transformers'a're provided with a common lead 46 which is grounded on the hull. The other terminal of secondary 44 is connected through condenser 42 to the neutral i5 and also through condenser 43 to the wire Iii which connects the two neutrals together. Thus the secondary 440i. the output transformer 24 is connected between ground and the two neutrals;

The other terminal of secondary" is connected to wires 41 and "which onshipboard maybe a tan circuit, or other available and suitable circuit, which in turn connect to the normal neutral system through the condensers 49 and 50 respectively by wire 46'. For purposes'of clarity it is noted that wire 46' is not one of the existing wiresof theships network, but is installed for the purpose. It is pointed out;that'a fan circuit normally differs from the ordinary lighting circuit in thatit originates in a single panelbox and exists as asingle circuit throu hout a large part of a ship. On the other hand, the individual" lighting circuitsnormally feed no more than four or five staterooms.

. quencies quite similarly to It is also noted that'other existing circuits on shipboard havingthis characteristic may be employed, such as telephone cir'- cults, bell signaling circuits, and other circuits of a similar nature, The loud speakers 24 in this case each have one terminal grounded to the hull, as ior example the partitions P as shown. The other terminal is connected between each adjacent normal" neutral and either the wire 41 or the wire48throu'gh the condensers Bland 6|.

This system operates quite similarly to that previously described. In case the normal neutral system is inoperative thespeake'rs are fed from the emergency neut condensers 52,154, '5; and 59, and thence back through the hull of the ship Hereagairr the al system through various short circuiting of one or more speakers does not interfere with the operation ofthe" remainder, of the system. Thesystem disclosed inthis flsl le is particularly useful in connection with two-wire or three-wire direct current systems commonly found on shipboard. Theivarious condenserspre vent the groundlngof. either theemr'ge'ncy .or

the normal systems through each other; The values of the various condensers employed are such as to permit the'pas'sage oithe signalirethe mannefrin which the condensers 32 and 33' actin' the alternatin current system ofFigure 1. These condensers prevent the interflow of power current between the two systems withoutfint' erfering with the interfiow of signal currents The system of Figure 3 is further modified in that the output of the amplifier? isprovided with four output transformers! In this case the normal neutr'ali is provided ,with the branches 10; 1|, 2"an'd 13; and jthe"emergency\neutral I5 is provided wlth the branches 14, 15 and 15. The speakers arebconnecte'd between the various neutrals through the transformers Hand 30 and thev condensers 32 andj33 as described in con-- nection with the systernof Figure, 1. ,One side of each of the primaries 'of' these-transformers is grounded' at 3|; 7 h is provided with four output transformers Si, 82, 83 and 8 4.' Their primaries are connected in seriesand the se condaries are connected so that one terminal of each is interconnected and provided with a common ground 85. The other terminalof each is connectedthr'ough the condensers 11, 18, 19, augmthe emergency neutrals 1E and 1 5, and the normal neutrals H and 12.

The 'connection between the normal and em rgency' 'neutral networks byIwire and impedance SI and switch cm series pfilmits an interfiow of power between thesystems." Im:

pedance 9| and; switch 80 "correspond to impedance 2| and switch 20 of Figure 1,. The op eration of the speakersisthesame as previously described; and the system provides independent circuits to each speaker I so that it will operate as previously described." ';j

A'modiflcation, adapted for use with the general system of this invention is shown in Figure 4. At this timeit is pointed out thatthe couplingtransformers 24 and 25frnay,be either the,

output transformers oi Ythe'amplifier which in the case of vacuum tube amplifiers would be connected in the plate circuits of the output vacuum tubes, or these coupling transformers may be additional transformers connected to the 1 output transformer The arrangement of ..,Figure I 4 clearlyillustrates them as beingthe output. trans-.

formers in the plate circuits of theffoutput vacuum tubes'VT. 'I'he output transformers are shown generally at'l24 and1l125. Theycomprise two partsecondaries I24 and 124' .anclil25 and;

The'butput' of the amplifier I25 respectively The transformers have the.

a single winding secondaries l 24 ."and .rejspecstounded lead 26.

the othercircuit.

tively. Each of. these secondaries has a common The other. terminals are connected to, the feeder wires I9 and I0'.as before which include the coupling condensers 21 and 23. With a connection of this type if a break or open circuit occurs in one lof the feeders I9 or1I0f near the amplifier theimpedance .of the transformer" in that circuit becomes relatively high causing a cor'rsiderabledoss in volume over For this reason it is desirable to have some means of automatically. short cirance with Figure arrangement. Suitable impedances such as the resistances I15 and I16 'ar e connected in series acrossthefe'eclers I9 and I0 in order to supply a' direct current path for the rectifier I30. .These resistances have a common connection to the groundedflcommonlead 26 through a condenser I 21. Likewiseconnected in series across these v feedersare a'pair' of magnets I28 and I29 with 'a common lead connected to ground through the condenser I21 and a rectifier I30. These magnets control a pair of switches I3! and I32. One contact of each of theseswitchesrespectively is connected to .thefeeders I9 and I0. The other contacts of each of theseswitches have a common connection to the ground lead 26. When an open circuit occurs on one of the feedthe voltageacross the associated magnet I29 or I28 .builds'up to close the associated switch. The closing of this entire sy'stern in operation. Thus switch I34 would control the microphone 22 and amplifier 23 and would close and. I32. Switch I34 controls the circuit comprising the wires I36 and I31 having a suitable current source I35. Thus if switch I34 is closed and feeder I 0' is open. circuited for any reason, magnet I28'would be energized to close switch I32 from opening thereby maintaining the short circuit acrossthe feeder I0 of the common lead 25. The net result of all this is that all the signal energy frorn'the amplifier will then go out over the circuit including. transformer I24 and will not be absorbed and lost in transformer I25.

in the feeder wires from theoutput transformer in an alternating current system. As before,

- voice signals.

'the coupling condensers H0 and these neutral systems may be interconnected by means of thefswitch' 20 through the inductance 2l. As before, the signal responsive devices or speakers. are connected in series with the secondaries ofa pair of transformers 29 and 30. In this case the primaries of these transformers are wound 1 in opposition and are connected across the main and emergency neutrals.

condenser 3I as distinguished from the pair of condensers 32 and 33; as. employed in the direct and emergency neutrals with respect to the power supply, it is not necessary to provide a pair -'of condensers in the leads to each of the primaries of the transformers 29 and 30.

Hence, a. single condenser in the groundqlead With the arrangement illustrated the supply of current from the amplifiers into the two channels is in parallel. The primaries of the speaker transformers are in parallel with respect to the feeders but series.

- accordance with this invention employing carrier frequencies which are modulated by the At'20I' is-disclosed a combined modulatorvand amplifier which is fed by means of the microphone 200 or other equivalent transmitter. At 202, 203 and 204 are diagrammatically illustrated control switches for the modulator amplifier, or transformers connected to the output terminals in the amplifier as previously described. I Y a The primaries are connected in series as are the secondaries which. are provided with the common grounding connection 201. These transformers feed into the lines 208 and 209 through 2II- as before. Feeder 208 is connected to' the emergency neutral EN of the emergency power system, and feeder 209 is connected to the mainneutral MN of the-main power supply system. As before, the inductance 2I2 and switch 2I3 are employed. The main and emergency neutrals extend to the panel boxes from which the branch neutrals. radiate. An emergencybranch neutral is indicated at EI and amain branch neutral is shown at MI. The reproducing devices TM are connected between pairs of'main and emergency neutrals the secondaries are in source. Thus the first reproducing deviceisconnected across the output terminals of a rectifier bridge 22]] the input terminals of which are fed by the secondaries of the transformers 2 and2l5. The terminals of'these secondaries are bridged by a tuned circuit ZI'S responsive to one of the carrier frequencies of the source. The primaries of these transformers are connected in series between, E! and Ml through the, condensers 2 l6 and 2|]. Theprimaries have a common grounded connection 2H3.v The arrangement for the second reproducing device only differs from the first in that the tuned circuit 219' is tuned to respondto another of 'the carrier fre quencies'. The third reproducingdevic'e'is shown connected to a rectifier bridge and supplied by anuntuned circuit so as to be operable by all of the carrierirequencies. a a

With this arrangement it will be apparent that when one. of the switches 202, 203 and 204' is closed the reproducing device will be, operated whose tuned circuit reSponds'tofthat particular frequency. When. another is closed anothe'rloffrequenciesso that it wil loperate when each of the others operates. ,7

It will be apparent to thoseskilled in the art that these principleslmay be employed in systerns employing a large number of reproducing devices andbe arranged so that a large-number of reproducing devices at difierents'paced points will be simultaneously operatedby a single one.

of the carrierfrequencies. The rectifiers employed in the: rectifying bridgesmay be of any suitable form available for the purpose, such as copper oxide rectifiers and the like, vacuum tube rectifiers, etc. r The system of Figure 7 illustrates a rather simplified form ofthe invention in which the basic principle of supplying energy from a common signal source over a plurality of channels to each of' a group of loud speakers is illustrated. As before, the main generatorsZ and 3 are shown grounded to the hull of the ship by meansfoffla connection which includes the impedance J. It is noted that in somecases theimpedancerepree sented by'l may be nothing more than the impedance of the grounding wire tothe hull. It is here emphasized, asis true of the other systems disclosed, that the principlesof the invention may be appliedfto networks which are not grounded. The emergency generators are'shown'byll and I2 in the superstructure of the ship.

The main neutral feeder. 6 is shown provided with the branch neutrals 6, 6 and 6 running to the various panel boxes 1B. The emergency neutral i5 is shown provided with thebranch neutrals I5 I5 and 'lii likewise'running to separate normal and emergency circuit l, panel boxes B. The switch 20 isprovidedas before to interconnect the main and branch neutralsin the normal operation of the main and emergency power systems. As before, a microphone or its equivalent 22 feeds into asuitable form of amplifier 23, one terminal of :which is grounded by the, wire 26 on the metal hull of theship. The other terminal is connectedfby the wire 2V to the main and emergency neutrals through the condensers 21 and 21 respectively. a The main branch neutrals 6*, B and 6 are shownrunning from the panel boxes to which the branch neutrals 6 and 6 extend. The emergency branch neutrals iii and IS are shown extending from the'panel-boxesto which'the emergency neutra-ls 15 and 15 extend. The main branch neutrals B), B and V, and the emergency branch neutrals l5? and l5 represent a fan or lightingjcircuit extending from the panel boxes.

A'feature of this form of the invention involves the interconnection of main branch neutrals to main branchfneutrals, emergency branch neutrals to emergency branch neutrals, and main brancnne'utrals to emergency branch neutrals. Thus condenser C connects the emergency branch neutral l5 to the mainbranch neutral G Condenser C connects the main branch neutral 6? to the main branch neutral 6*. Condenser C connectsthe 'main branch neutral 6 to the emergency branch neutral 15. Condenser 0 connects the main branch neutral'i to the emergencybranch neutral 15 Condenser C interconnects the emergency branchneutrals 15?? and I5Y'. The branch neutrals are notnormallyfinterconnected but" the above connections through condensers are made to produce a'systern in accordance withthe invention.

A series of signal responsive'dgvices, as for example loud speakers 34, 34', 34 34 34 34 34" and-34" areconnectedbetween'the various branch neutrals, main and emergency, to'ground on the metal walls or decks P of the ship through the condensers 33 'Circuits maybe trac'ed'to the reproducing devices 34*,*3 4 'and 34 over two channelsi" Energy is supplied from'the amplifier 23 to these speakers overthe circuit comprising the wires 15, and 6*. Energy is also fed from the amplifier over wire 6, wire 6 and wire 6 to whet}. Thus the ground ing or'opening of either of these separate circuits will not render more than one of these three speakers inoperative even then may a ground fromnear oneof the speakers,'and then onlyfthe speaker nearest that ground,

Thus with this'system in additionto providing safe and dependable operation under .all conditions, thecircuit arrangement is such that the volume level 'of the signals at the speakers is automatically distributed throughout the ent lre network. This is an exceedinglyimportant feaa direct short circuit of a 'speaker'can' affect only one of these speakers.

'The'application of the invention to a system where the main and emergency neutrals both extend to the same panel boxes is shown in connection with the speakers 34 -and 347. With this connection energy'is' fed over two-separate channels to these speakers from theemergency neutral 15 and'the main neutral 6. The interconnection between the branch emergency neutrals through the condenser C completes the circuits to the two speakers in'both' directions. Thus, for example if the emergency branch neutral IS 'isgrounded as indicated'at F, both'of these speakers will receive their energy over the neutral I5 throughthe condenser C An open circuit in either of these channels will not prevent the operation of both of the speakers.

It will be noted that in the arrangement of Figure '7 there] are three distinct combinations the others, or any two, as well as all three may be used. 1 Thus the main object of this invention of securing dependability under all possible conditions of operation is secured. From the above description it will be apparent that this invention resides in certain principles of arrangement and connection 'which may be embodied in other physical forms. without departure from thetrue scope thereof. We do not, therefore, desireto be strictlylimitedto the disclosure as given'iorpurposesof illustration, but rather to the scope of the appendedclaims. What we seek to'secure by United States Letters Patent is: I 1. In a signaling system the combination com prising a pair of grounded networks, a grounded signal source coupled to said network, for impressing a common signahcurrentflupon both of said networks, a plurality'of signal responsive devices each connected between said networks and each having a pair of grounded coupling d9? vices connectedbetween saidnetworks ior sup plying energy from the'network to said signal responsive devices simultaneously over two paths or over either path during an 'open circuit. or a short circuit on .the other. p r

2. In a signaling system of the type described the combination comprising a pair of grounded networks, a grounded, signal device coupled to the networks for supplying a common signal cursrent to both, a plurality of signal responsive devices, and means connected between each-of said networks and ground for supplyingenergy to said devices simultaneously over. two paths or over either. path during an opencircuit or a shortoir-I cuit on the other. I

3. In a signaling system the type described the combination comprising a pair of grounded networks, a grounded signal device connected to said networks for supplying a common signal current to both, a plurality of signal responsive devices, and low impedance means connected -be tween each of said networks and ground for supplying energy to said devices simultaneously over two paths or over either path during an open circuit or-a short circuit on the other.

4. In a signaling system of thetype described the combination comprising at least two grounded conductors, a grounded signal source connected to said conductors for applying a common signaling current to said conductors, and a plurality of signal responsive devices each connected between said conductors and ground whereby the signal current is supplied thereto over both conductors or ,over either during short circuit or open circuit on the other.

5. In a signaling system of the type described the combination comprising a grounded network, a grounded source of signal energy for applying a signal current to said'network at spaced points, a plurality of signal responsive devices, a pair of impedance means connected between spaced points on the network, means providing a common ground for said impedance devices, and means for connecting the signal responsive devices respectively to. said impedance devices.

6. In a signaling system the combination comprising a grounded conductive network, means for applyinga signaling current to said network at spaced points, a plurality 'of signal responsive devices, and grounded coupling devices for con.- necting said signal responsive devices to the network at spaced points, whereby signals reach each for grounding the'other, terminal signal responsive device over two different portionsoffsaid network.

7. In a signaling system the combination comprising a grounded conductive network, means for applying a signaling current to said networkat spaced points, a. plurality of signal responsive devices,'andmeans for' connecting said signal responsive devices to the network each comprising a transformer having its primary connected through acondenserto the network,'a common ground forthe primaries, and means for connecting each signai'fresponsive device in series with the secondaries of a pair of primaries having a common ground. v

8. In a signaling system the combination com-' prising a grounded conductive network, means for applying a signaling current to said' network at'spaced points, a plurality of signal responsive devices, means for. connecting'each signal responsive device'to the network" each comprising two device, being connected between ground and the mid-point of 'a' pair of said condensers,

9. I a signaling system the combination com: prising a grounded 'network, a source of signal energy having two output transformers, 'a coinmon ground for the secondaries of the'transformers, means for connecting th'e'other terminals of the secondaries to spaced points on the network, a plurality of signal responsive devices, and a pair of low impedance devices having a common ground and connected between spaced points on thejn'et'work forconnecting each signal responsive device to the network.

10. In a signaling, system on shipboard, the combination comprising a network composed oi! thegrounded neutrals of the main and emergency power'systems, grounded signal means forimpressinga common signal on both of said neutrals, a plurality of signal responsive devices, and low impedance means having a common ground and connected between the said neutrals for operating" therespective signal responsive devices.

11.- In a signaling system onshipboard, the combination comprising a network composed of the grounded neutrals of themain and emergency power systems, grounded signal means for 1m pressing a common signal on both of said neutrals, a pairof transformersfor each signal responsivedevice, means for connecting the prima-' ries of each pair'of transformers in series across the normal and emergency neutrals through condensers, a common g'roundfor the primaries, and

means for connecting the signalresponsive de-' pressing a common signal on both of said neutrals,

a pair of condensers connected in series across the normal and emergency neutrals for each sl gnal responsive device, a connectionfrom each signal responsive device to the common terminal of the associatedpair of, condensers, and means of the signal responsive device. t I

13. In a signaling system for use on shipboard, the combination comprising a network composed of the normal a'ndfemergency grounded power circuit neutrals, a source of energy having a pair of output transformers, a common ground for one terminal of each of the secondaries of the output transformers, means for connecting the other terminals of the secondaries to the net- 1 to said low impedance coupling meansfrespectively.

14. In a signaling system for use on shipboard, the combination comprising a grounded network composed of the neutral wires of the normal and emergency power circuits, means for generating a signal current having a plurality of output transformers, means for providing a common ground for the secondaries of all of said transformers, means for connecting the other terminals of the secondaries to the network at spaced points, a plurality of signal responsive devices, and means comprising a pair of grounded low impedance devices connected between the normal and emergency neutrals for coupling the signal responsive devices respectively to the network.

15. In a signaling system for use on shipboard, the combination comprising a network composed of the grounded neutrals of the main and emergency power systems, a grounded signal source, a pair of coupling transformers fed from said source, said transformers having a common ground for one terminal of each, means for connecting the other terminals of the transformers to the main and emergency neutral systems respectively, a plurality of grounded signal responsive devices each connected between the main and emergency neutral systems, and means for automatically short circuiting the secondaries of either of said coupling transformers upon the development of an open circuit in the means for connecting them to the main and emergency neutrals.

16. In a signaling system for use on shipboard, the combination comprising a conductive network composed of main andemergency power circuit neutrals, means for impressing signal energy upon the network thus formed, a plurality of signal. responsive devices, a pair of transformers for each of said devices,-the secondaries of each pair being connected in series with the associated device, the primaries of each pair of transformers being oppositely wound and connected in series across the main and emergency neutrals, and a common ground for the primaries having an impedance therein.

1'7. In a signaling system for use on shipboard and the like, the combination comprising a conductive network composed of main and emergency power neutrals, atransmitter for impressing signal energy upon the network thus formed, a plurality of signal responsive devices, a pair of transformers for each of said devices, the primaries of the transformers being connected in series between the main and emergencyneutrals and having a common ground, and connections between the secondaries of the associated pair of transformers and a signal responsive device.

18. In a signaling system the combination comprising a pair of separate conducting networks, means for interconnecting the-networks to .efiect signal energy transfer therebetween, a common source of signal energy connected to both networks to energize them, and a plurality of signal responsive devices connected to both of said networks whereby energy is supplied to each signal responsive device from both networks or from either upon failure of the other by short circuit.

19. In a signaling system the combination comprising a conductive network, an impedance connected into said network to isolate it substantially. into two portions with respect to the currents to be transmitted thereover; a grounded source of signal energy connected to the portions of the network on opposite sides'of said impedance, anda plurality of signal responsive devices connected between said portions of the network on opposite sides of saidimpedance whereby a common signal is transmitted to eachofsaid' devices over said a portions of the network." g

20. Ina signaling system the combination comprising a conductive network, an' impedance connected into said network to isolate it substantially into two portions with respect to thecurrents to be transmitted thereover, a grounded source of signal energy connected to the portions of the network on opposite sides of said impedance, a plurality of signal responsive devices, and grounded coupling means for each of the signal responsive devices for individually connecting them to said portions of the network.

21. In a signaling system the combination'comprising a conductive network, an impedance connected into said network to isolate it substantially:

into two portions with respect to the, currents to be transmitted thereover, a grounded source ofsignal energy connected to the portions of the 7 network on opposite sides of said impedance, a plurality of signal responsive devices, and grounded coupling means for each of the signal responsive devices for individually connecting them to said portions of the network, saidgrounded cou pling means comprising a pair of condensers connected'in series across said portions of the network and having their common points grounded.

22. In a signaling system the combination comprising a conductive network, an impedance connected into said network to isolate it substantially into two portions with respect to the'currents to be transmitted thereover, a grounded source of signal energy connected to the portions of the network on oppositesides of said impedance, a plucoupling means for each of the signal responsive devices for individually connecting them to said portions of the network, said means comprising a pair of transformers, the primaries of which are connected in series across the said portions of the network and havinga common ground, the signal responsive devices being respectively connected to the secondaries of said pairs of transformers in series therewith.

23. In a signaling system the combination comprising a conductive network, an impedance cone nected into said network to isolate it substantially into two portions with-respect to the currents to be-transmitted thereover, a groundedsource of signal energy connected to the portions of the network on opposite sides of said impedance, a

s plurality of'signal responsive devices, and gro nded coupling means for each of the-signal responrality of signal responsive devices, and grounded pointson'said network, a common source of sig- 75 nal energy, and means for, coupling the source to said network including a pair of transformers,

10 ously upon both of said channels, and a plurality of signal, responsive devices coupled to both of said channels including means for supplying curreniffrom both of said channels to'each of said devices simultaneously or from either of said channels during an open circ uitor a short circult on the other.

IRVING F. DURST.

SEMI JOSEPH 'BEGLIN;-//

f HERBERT BARNETT. 

